en 1-Power Systems Operation Power Systems Operation Research Paper Research Paper The main goal of this paper is to study statistical indices and evaluate AGC indices in power system which has large penetration of the WTGs. Increasing penetration of wind turbine generations, needs to study more about impacts of it on power system frequency control. Frequency control is changed with unbalancing real-time system generation and load . Also wind turbine generations have more fluctuations and make system more unbalance. Then AGC loop helps to adjust system frequency and the scheduled tie-line powers. The quality of AGC loop is measured by some indices. A good index is a proper measure shows the AGC performance just as the power system operates. One of well-known measures in literature which was introduced by NERC is Control Performance Standards(CPS). Previously it is claimed that a key factor in CPS index is related to standard deviation of generation error, installed power and frequency response. This paper focuses on impact of a several hours-ahead wind speed forecast error on this factor. Furthermore evaluation of conventional control performances in the power systems with large-scale wind turbine penetration is studied. Effects of wind speed standard deviation and also degree of wind farm penetration are analyzed and importance of mentioned factor are criticized. In addition, influence of mean wind speed forecast error on this factor is investigated. The study system is a two area system which there is significant wind farm in one of those. The results show that mean wind speed forecast error has considerable effect on AGC performance while the mentioned key factor is insensitive to this mean error. AGC,CPS,Load-Frequency Control,Wind Farm, 223 229 http://ijeee.iust.ac.ir/browse.php?a_code=A-10-804-5&slc_lang=en&sid=1 H. Rajabi Mashhadi h_mashhadi@um.ac.ir 180031947532846002924 180031947532846002924 Yes Ferdwosi University of Mashhad S. M. Eslami mahdi.eslami.84@stu-mail.um.ac.ir 180031947532846002925 180031947532846002925 No Ferdwosi University of Mashhad H. Modir Shanechi shanechi@iit.edu 180031947532846002926 180031947532846002926 No Illinois Institute of Technology